The bisdioxopiperazines including dexrazoxane (ICRF-187) are catalytic or non-cleavable complex-forming inhibitors of DNA topoisomerase II that do not produce DNA strand breaks. In this study we show that dexrazoxane inhibits the division of Chinese hamster ovary (CHO) cells resulting in marked increases in cell size (up to 80 micrometers in diameter), volume (up to 150-fold greater) and ploidy (as high as 32N). This last result indicates that the dexrazoxane-induced DNA reduplication was restricted to once per cell cycle. Kinetic analysis of flow cytometry data indicated that the conversion between successively higher ploidy levels was progressively slowed at longer times of exposure to dexrazoxane. Both the protein and DNA content of dexrazoxane-treated CHO cells increased linearly over time in the same proportion. Light and electron microscopic studies of dexrazoxane-treated cells showed ring-like multilobulated nuclei. Immunohistochemical staining of dexrazoxane-treated cells showed that F-actin and acetylated alpha-tubulin were present in large, highly organized networks. Furthermore, topoisomerase II co-localized with the DNA of the multilobulated nuclei. Staining for gamma tubulin revealed that the dexrazoxane-treated cells contained multiple centrosomes, indicating that this drug prevents cytokinesis but not centrosome reduplication. It is concluded that dexrazoxane inhibits CHO cytokinesis in cells by virtue of its ability to inhibit topoisomerase II.